Wireless communication system and method of controlling a transmission power

ABSTRACT

A base station is provided which notifies a mobile station of transmission power information for an uplink RACH, the mobile station transmits transmission delay estimation information on the RACH to the base station over the RACH at a transmission power based on the transmission power information, and the base station changes the transmission power information according to the transmission delay estimation information and notifies the mobile station of the changed transmission power information. The mobile station retransmits data or a preamble if the mobile station does not receive a notification that the base station has received the data or the preamble correctly after a predetermined time. The base station transmits the transmission power information over a BCH and a CPICH transmitted to a plurality of mobile stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 15/138,308 filed Apr. 26, 2016, which is a Continuation Applicationof U.S. application Ser. No. 13/943,950, filed Jul. 17, 2013, issued asU.S. Pat. No. 9,369,968 on Jun. 14, 2016, which is a ContinuationApplication of U.S. application Ser. No. 12/092,002 filed Apr. 29, 2008,issued as U.S. Pat. No. 8,515,480 on Aug. 20, 2013, which is 371 ofInternational Application No. PCT/JP2006/321981 filed Nov. 2, 2006,which claims priority from Japanese Patent Application No. 2005-321543filed Nov. 4, 2005, the contents of all of which are incorporated hereinby reference in their entirety.

TECHNICAL FIELD

The present invention relates to a transmission power control method fora wireless communication system transmitting data with wirelessresources shared among a plurality of mobile stations.

BACKGROUND ART

In a W-CDMA system, random access channels (RACHs) using Slotted ALOHAare present (see, for example, Non-Patent Document 1). A RACH is achannel for transmitting not wireless resources specific to andallocated to each mobile station but common wireless resources (afrequency band, a scrambling code, and time) shared among mobilestations in one cell. The RACH is a channel used to transmit signalsthat are relatively small in size and that are not transmittedcontinuously such as a control signal for notifying of a periodicmeasurement result or a control signal for requesting start of a datacommunication.

The RACH is constituted by two parts called a “preamble part” and a“message part”, and transmitted using orthogonal bit sequences called“signatures” so that a plurality of mobile stations can simultaneouslyaccess the RACH. 16 types of signatures are prepared, and each of themobile stations selects one from among these signatures at random anduses the selected signature for scrambling the preamble and selecting aspreading code of the message part. Accordingly, if the mobile stationsaccidentally select the same signature and start random accesses at thesame timing, collision of the message parts occurs. However, if mobilestations select different signatures, message parts can be received. Inthe latter case, however, a desired signal for one of the mobilestations becomes an interference signal for the other mobile station.Therefore, if the mobile stations transmit signals at the sametransmission power, a so-called near-far problem occurs. Namely, amobile station located farther from the base station, that is, a mobilestation having a greater propagation loss suffers a higher interferencefrom the other mobile station and a power for a desired wave attenuates,resulting in a greater deterioration in a signal to interference ratio(SIR).

Considering the near-far problem, as shown in FIG. 1, an open looptransmission power control is performed using preamble parts so thattransmission power is set to as small power as possible in a range inwhich an SIR of the message part from each mobile station satisfies adesired value at the base station. Specifically, the open looptransmission power control has the following procedures.

One mobile station transmits a preamble at a predetermined initial powervalue P_(init) [dBm]. At this time, a value calculated by the followingequation is set to the initial power value P_(init) [dBm] (see, forexample, Non-Patent Document 2).P _(init) =P_CPICH_Tx·CPICH_RSCP+UL_Interference+Constant_Value [dBm].

In the equation, P_CPICH_Tx [dBm] is a transmission power of a commonpilot signal (CPICH: Common Pilot Channel) transmitted from the basestation. UL_Interference and Constant_Value [dB] are predetermined poweroffsets and notified to each mobile station in a cell by a broadcastchannel or the like as system parameters common to the mobile stationsin the cell. Further, CPICH_RSCP [dBm] is a reception power level of theCPICH measured by each mobile station in a predetermined cycle.

As can be seen, the P_(init) is decided according to the CPICH_RSCH,thereby eliminating the influence of the difference in propagation lossas much as possible and setting a reception level constant at the basestation among the mobile stations.

Generally, however, a radio wave is susceptible to fading fluctuationgenerated by not only distance attenuation and shadowing but alsomovement of the mobile station in multipath environment. The fadingfluctuation varies according to a carrier frequency. Due to this, in aW-CDMA FDD system using different frequency bands between an uplink anda downlink, a propagation loss measured in a downlink CPICH does notalways coincide with that measured in an uplink CPICH. Moreover, becauseof presence of a measurement delay in the CPICH_RSCH, the propagationloss during transmission of a preamble greatly differs from that duringmeasurement of the CPICH_RSCP depending on the movement of the mobilestation, fading-caused drop or the like. Furthermore, the predeterminedconstants UL_Interference and Constant_Value are often set lower thanoptimum levels so as to suppress uplink interference. Due to suchfactors, a preamble reception power is insufficient and the base stationis often incapable of detecting the preamble.

If the base station can receive the preamble, the base station transmitsan acquisition indicator signal related to the preamble by a downlinkcommon control channel after passage of a predetermined time ΔTack froma preamble transmission timing. At this time, if the base stationpermits the mobile station transmitting the preamble to transmit amessage part, the base station transmits ACK to the base station. If thebase station does not permit the mobile station to transmit the messagepart for such reasons as excess of the number of mobile stations fromwhich the base station receives message parts, the base stationtransmits NACK to the mobile station.

On the other hand, the mobile station receives the downlink commoncontrol channel after passage of the predetermined time ΔTack from thepreamble transmission timing and receives the acquisition indicatorsignal indicating ACK, the mobile station transmits the message part tothe base station at a predetermined message part transmission timing. Ifthe mobile station receives the acquisition indicator signal indicatingNACK, then the mobile station notifies a higher layer of reception ofthe NACK and finishes the random access.

Furthermore, if the mobile station cannot receive the acquisitionindicator signal at the predetermined timing, this means that the basestation cannot receive the preamble. Therefore, the mobile stationretransmits the preamble to the base station after a predetermined time.At this time, the mobile station retransmits the preamble at a preambletransmission power P_(pre+tx)(k+1) [dBm] that is a previous transmissionpower P_(pre_tk)(k) plus a preamble power increment step ΔP_(p) [dB],i.e., performs so-called Ramp-up, where k indicates the number of timesof retransmission of the preamble (k is set to 0 (k=0) at initialtransmission).

The mobile station repeats the above-stated operations until receivingthe acquisition indicator signal or the number of times ofretransmission reaches a maximum number of times of retransmission Kdesignated as a system parameter.

Likewise, for an EUTRA (Evolved Universal Terrestrial Radio Access)system currently hotly debated in 3GPP, it is considered to introduceuplink random access channels (see, for example, Non-Patent Document 3).

In relation to the EUTRA system, a wireless access method based on FDMA(Frequency Division Multiple Access) has been mainly discussed andrandom access on the premise that only one mobile station transmitssignals in one frequency band and the like are considered. In this case,differently from the case where a plurality of mobile stations areallowed to access one channel in the same frequency band, the near-farproblem does not occur. Due to this, a fixed power value common to themobile stations in one cell can be set to a transmission power of eachmobile station. In this case, however, it is necessary to set thetransmission power so that the channel from even a mobile stationlocated at a cell end has a sufficiently high quality at the basestation. In other words, the mobile stations located at places otherthan the cell end transmit signals at excessive transmission power. Sucha state unfavorably and unnecessarily increases interference with theadjacent cells if two adjacent cells use the same frequency band.Moreover, this unfavorably and unnecessarily increases power consumptionof the mobile stations. Therefore, in the EUTRA, similarly to the WCDMA,it is preferable to make power setting based on the CPICH receptionmeasurement value so that a mobile station having a higher propagationloss has a higher transmission power. However, the EUTRA has a smallerdemerit of causing each mobile station to transmit a signal at excessivepower than the WCDMA by as much as absence of the near-far problem. Dueto this, it is proposed to set the transmission power so as to be ableto satisfy a desired quality from initial transmission and to reduce atransmission delay in the RACH without performing the so-called powerRamp-up of starting an initial power lower than the power that cansatisfy the desired quality and of gradually increasing the power asdone in the WCDMA.

-   [Non-Patent Document 1] 3GPP TS25.214 v6.6.0 (2005 June) 3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Physical layer procedures (FDD) (Release 6)-   [Non-Patent Document 2] 3GPP TS25.331 v6.6.0 (2005 June) 3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Radio Resource Control (RRC); Protocol Specification    (Release 6)-   [Non-Patent Document 3] 3GPP TS25.814 v0.2.0 (2005 August) 3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Physical Layer Aspects for Evolved UTRA (Release 7)

DISCLOSURE OF THE INVENTION Problems to be Solved

However, the RACH transmission power control exerted in the WCDMA systemor the EUTRA system stated above has the following problems.

Although the RACH transmission power is decided based on the valuedesignated by the base station (the power offset during the open looppower control or the fixed power value common to one cell), it isdifficult to set the value to an optimum value. The reason is asfollows. Since the interference varies depending on the situation of thecell to which the mobile station belongs or that of the adjacent cell,the transmission power necessary to obtain a desired SIR at the basestation differs according to the situation. Furthermore, since the datatransmission starts under the initiative of each mobile station over therandom access channel, the base station cannot recognize that one mobilestation tries to transmit a RACH until the base station receives theRACH correctly. The difficulty is, therefore, that the transmissionpower cannot be adaptively controlled according to the situation oftransmission of the RACH. If the RACH transmission power is notappropriately set, the following problems occur.

1. RACH Transmission Power is Too Low

The problems disadvantageously occur that the number of times ofretransmission required until a RACH is correctly received increases,the transmission delay of the RACH increases, and that service qualitydegrades. If the power Ramp-up is not performed, in particular, theRACHs can be transmitted always at a constant power whether receptionfails. Due to this, the RACH can be retransmitted only in a state ofinsufficient power, resulting in a situation in which the RACH cannot becorrectly received even by as much as the maximum number of times ofretransmission at worst and in communication failure.

2. RACH Transmission Power is Too High

The problem occurs that an interference of one mobile station with anadjacent cell or the other users (in case of the WCDMA) in the cell towhich the mobile station belongs increases. Besides, there is a problemof an increase in power consumption of each mobile station.

It is, therefore, an object of the present invention to provide atransmission power control method for a wireless communication systemthat enables a base station to appropriately set a power of a RACH thatis common wireless resources according to a situation in the cell.

Means for Solving the Problems

To solve the problem, the present invention provides a method ofcontrolling a transmission power, causing a base station to control atransmission power of a mobile station, comprising: causing the basestation to notify of transmission power information on a RACH of anuplink; causing the mobile station to transmit transmission delayestimation information on the RACH at transmission power set based onthe transmission power information over the RACH; and causing the basestation to change the transmission power information on the RACHaccording to the transmission delay estimation information, and tonotify the mobile station of the changed transmission power informationon the wireless channel. Furthermore, the mobile station to retransmitdata or a preamble after a predetermined time since transmitting thedata or the preamble over the RACH if the mobile station does notreceive an ACK which is a notification of which the base station hasreceived the transmitted data or preamble correctly.

The mobile station notifies of the number of the transmission or theretransmission of the data or the preamble, a time elapsed since initialtransmission of the data or the preamble or a timing of initialtransmission of the data or the preamble by the transmission delayestimation information.

The mobile station retransmits the data or the preamble at atransmission power increased by a predetermined increase step if themobile station does not receive the acquisition indicator information.The base station increases the transmission power of the RACH if astatistic value based on the transmission delay estimation informationis greater than a predetermined target value.

The mobile station decides the transmission power of the RACH accordingto a reception power of a pilot signal transmitted from the basestation. Further, the mobile station resets the transmission delayestimation information if the mobile station receives the acquisitionindicator information.

By executing the above-stated sequence steps, the base station canappropriately set the RACH power according to a situation in the cell.

Advantages of the Invention

According to the present invention, the base station can appropriate setthe RACH power. It is also possible to reduce the transmission delay ofthe RACH. It is also possible to reduce the interference of a mobilestation with the other cell or with the other users in the cell to whichthe mobile station belongs. Due to this, throughput and capacity of theentire system can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of an open loop transmission powercontrol.

FIG. 2 is a conceptual diagram of a system according to the presentinvention.

FIG. 3 is a sequence diagram of the system according to the presentinvention.

FIG. 4 is a sequence diagram of the system according to the presentinvention.

FIG. 5 is a configuration diagram of a mobile station according to afirst embodiment.

FIG. 6 is a flowchart of the mobile station according to the firstembodiment.

FIG. 7 is a flowchart of the mobile station according to the firstembodiment.

FIG. 8 is a configuration diagram of a base station according to thefirst embodiment.

FIG. 9 is a flowchart of the base station according to the firstembodiment.

FIG. 10 is a flowchart of a mobile station according to a fifthembodiment.

FIG. 11 is a flowchart of a mobile station according to a sixthembodiment.

FIG. 12 is a flowchart of a base station according to the sixthembodiment.

FIG. 13 is a configuration diagram of a mobile station according to aseventh embodiment.

FIG. 14 is a flowchart of the mobile station according to the seventhembodiment.

DESCRIPTION OF REFERENCE SYMBOLS

-   11 reception processing unit-   12 signal separation unit-   13 pilot signal measurement unit-   14 power calculation unit-   15 acquisition indicator signal determination unit-   16 number-of-transmission measurement unit-   17 buffer-   18 signal combining unit-   19 transmission processing unit-   20 preamble generation unit-   21 reception processing unit-   22 decoding unit-   23 error determination unit-   24 signal separation unit-   25 number-of-transmission calculation unit-   26 power offset control unit-   27 control signal generation unit-   28 signal combining unit-   29 transmission processing unit

BEST MODE FOR CARRYING OUT THE INVENTION

Most preferred embodiments of the present invention will be describedhereinafter with reference to the drawings. The embodiments will bedescribed assuming that a system is an E-UTRA system now underconsideration in the 3GPP.

FIG. 2 is a conceptual diagram of a system to which the presentinvention is applied. In the system, a plurality of base stations arepresent adjacently to one another, a plurality of mobile stationstransmit or receive data on a downlink or an uplink to or from each ofthe base stations, OFDM (Orthogonal Frequency Division Multiple Access)is used for the downlink, and FDMA is used for the uplink. Furthermore,each of the mobile stations and base stations realizes functions to bedescribed below by a control program stored in a memory of each of themobile stations and base stations.

Each base station transmits on the downlink at least:

a broadcast channel (BCH) for transmitting broadcast information such assystem information,

a common pilot channel (CPICH) for transmitting a pilot signal, and

an acquisition indicator channel (AICH) for transmitting acquisitionindicator information in response to uplink data transmission.

FIG. 3 is a sequence diagram of the system. One mobile station transmitsor receives data based on the system information transmitted over theBCH. Further, the mobile station receives the CPICH in a predeterminedcycle to ensure synchronization and measures a reception quality of theCPICH. Moreover, if user data or a control signal (hereinafter,generically “data”) to be transmitted occurs to the mobile station, themobile station transmits the data using a random access channel (RACH)that is one of uplink wireless channels. This corresponds totransmission of the message part in the RACH transmission described inthe “BACKGROUND ART” part. A RACH transmission power at this time isdecided based on a value indicated by the base station using the BCH.

If the mobile station transmits the data over the RACH, the mobilestation receives an acquisition indicator signal over the AICH after apredetermined time. The mobile station retransmits data at apredetermined timing until the mobile station receives an acquisitionindicator signal (ACK signal) indicating that the data transmitted fromthe mobile station has been correctly received or until the number oftimes of retransmission reaches a predetermined maximum number of timesof retransmission.

FIG. 4 shows another exemplary sequence of the system. FIG. 4 differsfrom FIG. 3 in the following respect. Similarly to the “BACKGROUND ART”part described above, if data to be transmitted occurs to the mobilestation, the mobile station transmits a preamble over the RACH first. Ifthe base station correctly receives the preamble, the base stationtransmits an acquisition indicator signal (ACK signal) over the AICHafter a predetermined time. After receiving the acquisition indicatorsignal over the AICH, the mobile station transmits data or the preamble.It is to be noted that the preamble is a bit pattern known to the basestation, and that a signal unknown to the base station such as user dataor a control signal is not transmitted as the preamble.

In each of these sequences, the mobile station also transmitstransmission delay estimation information while adding the transmissiondelay estimation information to the data or the preamble over the RACH.By doing so, the base station can control information on the RACHtransmission power indicated by the BCH so that a delay required untilthe data or preamble is correctly received can be controlled to anappropriate value. It is possible to reduce interference by setting thetransmission power of the mobile station as low as possible whileeffectively reducing the data transmission delay.

First Embodiment

Features of a first embodiment are as follows.

-   1. A mobile station transmits the number of times of retransmission    or the number of times of transmission of the RACH as the    transmission delay estimation information. In this case, the    relationship between the number of times of retransmission and the    number of times of transmission is (the number of times of    retransmission)=(the number of times of transmission)−1. Embodiments    will be described hereinafter assuming that the number of times is    the number of times of transmission.-   2. A base station notifies of a power offset as information on a    RACH transmission power, and the mobile station decides the RACH    power based on a CPICH reception power and the power offset (open    loop power control).-   3. The mobile station retransmits data at the same power as that    used during data transmission.-   4. The mobile station transmits data while adding the transmission    delay estimation information to the data during the data    transmission shown in FIG. 3. First to sixth embodiments will be    described while referring to the system shown in FIG. 3.

By the above-stated features, the base station can determine whether theaverage number of times of transmission until each of the mobilestations in the system can correctly receive data over the RACH is keptto a desired level. If the average number of times of transmission islarge, the power offset of the RACH can be controlled to be increased soas to reduce the transmission delay.

FIG. 5 shows a configuration of each of the mobile stations according tothe first embodiment. The mobile station according to the firstembodiment is configured to include a reception processing unit 11receiving a downlink signal and performing a necessary receptionprocessing such as FET (Fast Fourier Transform), a signal separationunit 12 separating signals in respective channels from the receivedsignal, a pilot signal measurement unit 13 measuring a power intensityof a separated pilot signal, a power calculation unit 14 calculating apower of the RACH, an acquisition indicator signal determination unit 15determining an acquisition indicator signal received over an AICH, anumber-of-transmission calculation unit 16 counting the number of timesof transmission of the RACH, a buffer 17, a signal combining unit 18combining uplink data with a control signal, and a transmissionprocessing unit 19 performing a processing necessary for signaltransmission.

The signal separation unit 12 separates signals in respective channelsfrom the signal subjected to the reception processing. The signalseparation unit 12 transmits a CPICH signal to the pilot signalmeasurement unit 13, an AICH signal to the acquisition indicator signaldetermination unit 15, and a BCH signal to the power calculation unit14.

The pilot signal measurement unit 13 measures a pilot signal averagereception power in a predetermined cycle and transmits the measuredaverage reception power to the power calculation unit.

The power calculation unit 14 calculates a RACH transmission power P_Txfrom a CPICH transmission power CPICH_Tx notified by the BCH, a poweroffset PO, and the pilot signal average reception power CPICH_Rx, andnotifies the transmission processing unit 19 of the calculated RACHtransmission power P_Tx.

The acquisition indicator signal determination unit 15 determineswhether an ACK signal is received as the acquisition indicatorinformation, and notifies the number-of-transmission calculation unit 16and the buffer 17 of a determination result.

If the mobile station receives the ACK signal, thenumber-of-transmission calculation unit 16 resets the number of times oftransmission to 0. If the mobile station does not receive the ACKsignal, the number-of-transmission calculation unit 16 increases thenumber of times of transmission by 1 and notifies the signal combiningunit 18 of the increased number of times of transmission.

If the mobile station receives the ACK signal, the buffer 17 abandonsthe relevant data. If the mobile station does not receive the ACKsignal, the buffer 17 transmits the relevant data to the signalcombining unit 18.

The signal combining unit 18 combines the data transmitted from thebuffer with the number-of-transmission information, and transmits theresultant data to the transmission processing unit 19.

FIG. 6 is a flowchart if the mobile station transmits data using theRACH according to the first embodiment.

The reception processing unit of the mobile station receives the BCH(step 11), and receives the CPICH transmission power CPICH_Tx, the poweroffset PO, the maximum number of times of transmission and the liketransmitted as the system information. The pilot reception powermeasurement unit measures the pilot signal average reception powerCPICH_Rx in the predetermined cycle (step 12). If transmission data isstored in the buffer (step 13), the number-of-transmission calculationunit sets the number-of-transmission information to 1 (step 14),calculates the RACH transmission power P_Tx (step 15), and transmits thenumber-of-transmission information as well as the data over the RACH(step 16). At this time, the power calculation unit calculates the RACHtransmission power P_Tx according to the following equation.P_Tx=CPICH_Tx−CPICH_Rx+PO[dBm]

After the predetermined time, the mobile station receives the downlinkAICH (step 17). If the mobile station receives the ACK signal as theacquisition indicator information, the processing is returned to thestep 11 (step 18; YES). If the mobile station does not receive the ACKsignal, then the number-of-transmission calculation unit increase thenumber-of-transmission information by 1 (step 19), the processing isreturned to the step 15, and the mobile station transmits the same dataas the data transmitted previously. The mobile station repeats theoperations until the mobile station receives the ACK signal over theAICH transmitted after the predetermined time since data transmission oruntil the number of times of transmission reaches the predeterminedmaximum number of times of transmission.

FIG. 7 shows another example of the data transmission control exerciseby the mobile station using the RACH.

The reception processing unit of the mobile station receives the BCH(step 20), and receives the CPICH transmission power CPICH_Tx, the poweroffset PO, the maximum number of times of transmission and the liketransmitted as the system information. The pilot reception powermeasurement unit measures the pilot signal average reception powerCPICH_Rx in the predetermined cycle (step 21). If transmission data isstored in the buffer (step 22), the number-of-transmission calculationunit sets the number-of-transmission information to 1 (step 23),calculates the RACH transmission power P_Tx (step 24), and transmits thenumber-of-transmission information as well as the data using the RACH(step 25).

After the predetermined time, the mobile station receives the downlinkAICH (step 26). If the mobile station receives the ACK signal as theacquisition indicator information, the processing is returned to thestep 20 (step 27; YES). If the mobile station does not receive the ACKsignal, the mobile station receives the BCH and CPICH again (step 28).If system information is the same as the previously received systeminformation (step 29; YES), then the number-of-transmission calculationunit increase the number-of-transmission information by 1 (step 30), theprocessing is returned to the step 24, and the mobile station transmitsthe same data as the data transmitted previously. Thereafter, the mobilestation receives the system information over the BCH. If a value of eachof or one of the CPICH transmission power and the power offset includedin the system information differs from the previous value (step 29; NO),the processing is returned to the step 23, where thenumber-of-transmission calculation unit sets the number-of-transmissioninformation to 1, and the mobile station transmits newly received data.The mobile station repeats the operations until the mobile stationreceives the ACK signal over the AICH transmitted after thepredetermined time since data transmission or until the number of timesof transmission reaches the predetermined maximum number of times oftransmission.

FIG. 8 shows a configuration of each of the base stations used in thefirst embodiment. The base station used in the first embodiment isconfigured to include a reception processing unit 21, a decoding unit22, an error determination unit 23, a signal separation unit 24separating a signal, a number-of-transmission calculation unit 25, apower offset control unit 26, a control signal generation unit 27, asignal combining unit 28, and a transmission processing unit 29.

The error determination unit 23 checks whether a data block includingthe data and the number-of-transmission information has no error by aCRC added to the data block. If the base station can receive the datablock without an error, the error determination unit 23 transmits theACK signal to the signal combining unit 28 and the data block to thesignal separation unit 24.

The signal separation unit 24 transmits the number-of-transmissioninformation to the number-of-transmission calculation unit 25, and thedata to a higher layer.

The number-of-transmission calculation unit 25 collects thenumber-of-transmission information on the respective base stations andrecords the information in a memory (not shown). Further, thenumber-of-transmission calculation unit 25 calculates an average valueof the number of times of transmission (hereinafter, “average number oftimes of transmission) recorded in the memory at a predetermined poweroffset update timing, transmits a calculation result to the power offsetcontrol unit 26, and erases the number-of-transmission informationrecorded in the memory.

The power offset control unit 26 updates the power offset so that theaverage number of times of transmission nears a desired target averagenumber of times of transmission, and transmits an update result to thesignal combining unit 28.

The control signal generation unit 27 generates the common pilot signaland signals related to other system control information, and transmitsthe generated signals to the signal combining unit 28.

The signal combining unit 28 maps the transmitted signals on respectivechannels of the CPICH, the BCH, and the AICH, combines the signals, andtransmits the combined signal to the transmission processing unit 29.

FIG. 9 is a flowchart if the base station updates the power offsetaccording to the first embodiment.

The base station notifies of the power offset as the system informationin a predetermined cycle over the BCH (step 31), receives an uplink RACH(step 32), and checks whether the uplink RACH is received successfullyby the CRC after a reception processing (step 33). If the receptionsucceeds, the base station transmits the ACK signal over the AICH (step34). Further, the base station extracts the number-of-transmissioninformation from the successfully received data block and records thenumber-of-transmission information in the memory (step 35). If timing isthe predetermined power offset update timing (step 36), the base stationcalculates the average value of the number of times of transmission ofthe mobile stations in one cell extracted so far (step 37), and updatesthe power offset so that the average number of times of transmissionnears the desired target average number of times of transmission.

Assuming, for example, that the average number of times of transmissionis N_ave, the target number of times of transmission is N_target, thecurrent power offset is PO_current, the updated power offset isPO_update, a power offset increase step is Δup(Ramp-up), and a poweroffset decrease step is Δdown(Ramp-down), the following relationshipsare held.

If N_ave>N_target,

PO_update=PO_current+Δup [dB] (step 38).

If N_ave<N_target,

PO_update=PO_current·Δdown [dB] (step 39).

It is assumed herein that the relationship of Δup and Δdown isΔup>Δdown.

The base station notifies each base station in the cell of the updatedPO over the BCH (step 40).

In this manner, if the average number of times of transmission isgreater than the predetermined target number, the power offset can beincreased. Accordingly, the RACH transmission power of each mobilestation in the cell is set high and the reception quality of the RACH atthe base station is improved. It is, therefore, possible to reduce thenumber of times of transmission before the RACH is receivedsuccessfully, and reduce the transmission delay. Moreover, if theaverage number of times of transmission is smaller than thepredetermined target number, that is, the RACH is transmitted atexcessive quality, the power offset can be reduced. Accordingly, theRACH transmission power of each mobile station in the cell is set highand the interference with the other cells can be reduced.

As stated so far, according to the first embodiment, each mobile stationnotifies the base station of the number-of-transmission information aswell as the RACH at the time of transmission of the RACH. Accordingly,if the average number of times of transmission is greater than thepredetermined target value, that is, a delay before the data is receivedcorrectly over the RACH is great, then the power offset is increased soas to set the RACH transmission power high and each mobile station inthe cell can be notified of the increased power offset. By doing so, theRACH transmission power of each mobile station in the cell increases andthe probability that the base station can correctly receive dataincreases, so that the average number of times of transmission decreasesand the RACH transmission delay can be reduced.

If the average number of times of transmission is smaller than thepredetermined target value, this means that each mobile stationtransmits the RACH at excessive quality. Due to this, the power offsetis decreased so that the RACH transmission power is set low, and eachmobile station in the cell can be notified of the decreased poweroffset. It is, therefore, possible to reduce the RACH transmissionpower, reduce the interference with the other cells, and reduce thepower consumption of each mobile station.

Furthermore, according to the first embodiment, the power offsetincrease step and the power offset decrease step are set asymmetric sothat the power offset increase step is greater than the power offsetdecrease step. By so setting, if the delay is great, the power can bepromptly increased. Since the subsequent reduction is made gradually, ittakes longer time until the delay becomes greater (that is, the averagenumber of times of transmission is greater than the target number oftimes of transmission). A target delay can be, therefore, stablysatisfied. However, embodiments of the present invention are not limitedto the first embodiment. Namely, the power offset increase step and thepower offset decrease step may be set to an identical value, and thedecrease step may be set greater than the increase step.

Second Embodiment

A second embodiment differs from the first embodiment in the followingrespects. Each of the base stations also notifies a RACH power increasestep ΔP over the BCH. Each of the mobile stations receives informationon the power increase step ΔP as well as the CPICH transmission powerCPICH_Tx and the power offset PO over the BCH, calculates the RACHtransmission power P_Tx according to the following equation, andretransmits the RACH with a power increased from the previous power byΔP [dB].P_Tx=CPICH_Tx·CPICH_Rx+PO+ΔP×((number of times of transmission)−1) [dBm]

If the number of times of retransmission is used, ((number of times oftransmission)−1) is replaced by ((number of times of retransmission)−1).

At this time, if the mobile station is to transmit new data over theRACH after receiving the ACK signal over the AICH, the mobile stationtransmits the new data with the power returned to initial power obtainedfrom the power offset and the CPICH reception power. The otheroperations are similar to those according to the first embodiment.

Third Embodiment

A third embodiment differs from the first embodiment in the followingrespects. In the first embodiment, the RACH power value is decided basedon the CPICH reception power and the power offset. In the thirdembodiment, each of the base stations notifies each mobile station of afixed transmission power value P_Tx as system information, and each ofthe mobile stations in the cell transmits the RACH at P_Tx. The basestation increases or decreases P_Tx by a predetermined step according tothe number of times of transmission notified from the mobile station.Specifically, the base station calculates P_Tx as follows.

Assuming that the average number of times of transmission is N_ave, thetarget number of times of transmission is N_target, the currenttransmission power is P_Tx_current, the updated transmission power isP_Tx_update, a power increase step is Δup, and a power decrease step isΔdown, the following relationships are held.

If N_ave>N_target,

P_Tx_update=P_Tx_current+Δup [dB].

If N_ave<N_target,

P_Tx_update=P_Tx_current−Δdown [dB].

The P_Tx updated at the base station is notified to the mobile stationas the system information over the BCH. The other operations are similarto those according to the first embodiment.

Fourth Embodiment

A fourth embodiment is a combination of the second and thirdembodiments. In the second embodiment, the RACH initial transmissionpower value is decided based on the CPICH reception power and the poweroffset. In the fourth embodiment, each of the base stations notifieseach mobile station of the fixed transmission power value P_Tx as systeminformation, and each of the mobile stations in the cell transmits aninitial RACH at P_Tx. Thereafter, in case of retransmission, the mobilestation retransmits the RACH at a power obtained by adding apredetermined power increase step ΔP to P_Tx. Furthermore, the basestation increases or decreases the fixed transmission power value P_Txby a predetermined step according to the number of times of transmissionfrom the base station in the manner described in the first embodiment,and notifies the mobile station of the resultant transmission power asthe system information over the BCH. The other operations are similar tothose according to the first or second embodiment.

Fifth Embodiment

In a fifth embodiment, each of the mobile stations causes a timer tooperate at time of initial RACH transmission, and notifies each of themobile stations of a value of the timer during retransmission, that is,a time elapsed from start of RACH transmission as transmission delayestimation information.

FIG. 10 is a flowchart if each of the mobile stations transmits datausing the RACH according to the fifth embodiment.

The mobile station receives the BCH (step 41), receives the CPICHtransmission power CPICH_Tx, the power offset PO, the maximum number oftimes of transmission and the like transmitted as the systeminformation, and measures the pilot signal average reception powerCPICH_Rx in the predetermined cycle (step 42). If transmission data ispresent (step 43), the timer is started at 0 (step 44).

The mobile station transmits timer information as well as the data overthe RACH at the transmission power P_Tx (step 45). After thepredetermined time, the mobile station receives the downlink AICH (step46). If the mobile station receives the ACK signal (step 47; YES), thetimer is stopped (step 48), and the processing is returned to the step41. If the mobile station does not receive the ACK signal, then theprocessing is returned to the step 45, and the mobile stationretransmits the timer information as well as the data transmittedpreviously. The mobile station repeats the operations until the mobilestation receives the ACK signal over the AICH transmitted after thepredetermined time since data transmission or until the number of timesof transmission reaches the predetermined maximum number of times oftransmission.

Sixth Embodiment

In a sixth embodiment, using system time known to base stations andmobile stations, each mobile station notifies one base station of systemtime that is RACH transmission start time, and the base stationcalculates a transmission delay by subtracting system time that is thenotified transmission start time from system time at which the RACH isreceived successfully.

FIG. 11 is a flowchart if each of the mobile stations transmits datausing the RACH according to the sixth embodiment.

The mobile station receives the BCH (step 51), receives the CPICHtransmission power CPICH_Tx, the power offset PO, the maximum number oftimes of transmission and the like transmitted as the systeminformation, and measures the pilot signal average reception powerCPICH_Rx in the predetermined cycle (step 52). If transmission data ispresent (step 53), current system time T_init is recorded (step 54).

The mobile station transmits system time as well as the data over theRACH at the transmission power P_Tx (step 55). After the predeterminedtime, the mobile station receives the downlink AICH (step 56). If themobile station receives the ACK signal (step 57; YES), the recordedsystem time is deleted (step 58), and the processing is returned to thestep 51. If the mobile station does not receive the ACK signal, theprocessing is returned to the step 55, and the mobile stationretransmits the system as well as the data transmitted previously. Themobile station repeats the operations until the mobile station receivesthe ACK signal over the AICH transmitted after the predetermined timesince data transmission or until the number of times of transmissionreaches the predetermined maximum number of times of transmission.

FIG. 12 is a flowchart if the base station updates the power offsetaccording to the sixth embodiment.

The base station notifies of the power offset as the system informationin a predetermined cycle over the BCH (step 60), receives an uplink RACH(step 61), and checks whether the uplink RACH is received successfullyby the CRC after a reception processing (step 62). If the receptionsucceeds, the base station records current system information T_current(step 63) and transmits the ACK signal over the AICH (step 64). Further,the base station extracts system time information T_init from thereceived block, calculates transmission delay time T=(T_current−T_init),and records the transmission delay time T=(T_current−T_init) in thememory (step 65). If timing is the predetermined power offset updatetiming (step 66), the base station updates the power offset based on thetransmission delay time calculated and recorded so far. By way ofexample, the base station calculates average transmission delay time(step 67) and updates the power offset so that the average transmissiondelay time nears a desire target value.

Assuming, for example, that the average transmission delay time isT_ave, the target transmission delay time is T_target, the current poweroffset is PO_current, the updated power offset is PO_update, the poweroffset increase step is Δup, and the power offset decrease step isΔdown, the following relationships are held.

If T_ave>T_target,

PO_update=PO_current+Δup [dB] (step 68).

If T_ave<T_target,

PO_update=PO_current−Δdown [dB] (step 69).

It is assumed herein that the relationship of Δup and Δdown isΔup>Δdown.

The base station notifies each base station in the cell of the updatedPO over the BCH (step 70).

Seventh Embodiment

A seventh embodiment is used in a system transmitting data using themessage part after transmitting the preamble as described with referenceto FIG. 4. Transmission delay estimation information is not transmittedusing a preamble before reception of the ACK signal, but thetransmission delay estimation information is transmitted when a preambleor data after reception of the ACK signal is transmitted with thetransmission delay information added to the preamble or the data.

The operations according to the first to sixth embodiment can be appliedto the other operations. In the seventh embodiment, the number of timesof transmission of the preamble is used as the transmission delayinformation, and calculation of the RACH power is decide based on theCPICH transmission power, the CPICH reception power, the predeterminedpower offset, and the number of times of transmission as described inthe second embodiment. For example, in FIG. 1, the message part istransmitted after the preamble is transmitted three times. Therefore,“(number of times of transmission)=3” is transmitted as the transmissiondelay information using the message part.

FIG. 13 shows a configuration of each of the mobile stations accordingto the seventh embodiment. The configuration of the mobile stationaccording to the seventh embodiment differs from that according to thefirst embodiment (FIG. 5) in that a preamble generation unit isadditionally included in the mobile station.

If data arrives at the buffer, then the buffer notifies the preamblegeneration unit of data arrival, the preamble generation unit generatesa predetermined bit sequence, transmits the generated bit sequence tothe signal combining unit, and notifies the number-of-transmissionmeasuring unit that the preamble is transmitted to thenumber-of-transmission measuring unit. The transmission processing unitperforms a necessary processing on the generated bit sequence and thentransmits the processed bit sequence as a preamble.

Furthermore, the acquisition indicator signal determining unit notifiesthe preamble generation unit whether or not the acquisition indicatorsignal determining unit receives the ACK signal over the AICH afterpredetermined time since transmission of the preamble.

If the acquisition indicator signal determining unit does not receivethe ACK signal, the preamble generation unit generates the predeterminedbit sequence and transmits the generated bit sequence as the preamblesimilarly to the above. Further, the preamble generation unit notifiesthe number-of-transmission measuring unit of transmission of thepreamble. In response to the notification of the transmission of thepreamble, the number-of-transmission measuring unit increases therecorded number of times by 1.

If the acquisition indicator signal determining unit receives the ACKsignal, the preamble generation unit does not generate the preamble andnotifies the number-of-transmission measuring unit that transmission ofthe preamble is stopped. In response to the notification of the stop ofthe transmission of the preamble, the number-of-transmission measuringunit transmits the recorded number of times of transmission to thesignal combining unit as the number-of-transmission information.Further, the buffer is also notified that the acquisition indicatorsignal determining unit receives the ACK signal, and the buffertransmits a data block to the signal combining unit, accordingly.

The signal combining unit combines the data block with thenumber-of-transmission information, and the transmission processing unitperforms a necessary processing on the number-of-transmissioninformation and then transmits the processed information.

FIG. 14 is a flowchart if each of the mobile stations transmits datausing the RACH according to the seventh embodiment.

In the mobile station, the reception processing unit receives the BCH(step 71), and receives the CPICH transmission power CPICH_Tx, the poweroffset PO, the maximum number of times of transmission and the liketransmitted as the system information. The pilot reception powermeasurement unit measures the pilot signal average reception powerCPICH_Rx in the predetermined cycle (step 72). If transmission data isstored in the buffer (step 73), the number-of-transmission calculationunit sets the number-of-transmission information to 1 (step 74),calculates the RACH transmission power P_Tx (step 75), and transmits thepreamble over the RACH (step 76). At this time, the power calculationunit calculates the RACH transmission power according to the followingequation.P_Tx=CPICH_Tx−CPICH_Rx+PO+Δp×((number of times of transmission)−1) [dBm]

After the predetermined time, the mobile station receives the downlinkAICH (step 77). If the mobile station receives the ACK signal as theacquisition indicator information (steps 78 and 80; YES), then themobile station transmits the data and the number-of-transmissioninformation over the RACH (step 81), and the processing is returned tothe step 71. If the mobile station does not receive the ACK signal andthe number of times of transmission is smaller than the maximum numberof times of transmission (step 78; NO), then the number-of-transmissioncalculation unit increases the number-of-transmission information by 1(step 79), and the processing is returned to the step 75. Furthermore,if the mobile station does not receive the ACK signal and the number oftimes of transmission reaches the maximum number of times oftransmission (step 80; NO), the processing is returned to the step 71.

In the first to seventh embodiments stated above, data is transmittedusing the RACH. However, the data is not limited to user data. Forexample, a resource reservation request signal for requesting allocationof uplink wireless resources for transmitting the user data may betransmitted using the RACH. Alternatively, the transmission of datausing the RACH may be applied to an instance of transmitting a controlsignal necessary to transmit downlink data, e.g., a signal notifying ofa quality of a downlink wireless channel (CQI: Channel QualityIndicator) or the like.

In the first to seventh embodiments stated above, the OFDM and the FDMAare used for the downlink and the uplink as the wireless access methods,respectively. However, the scope of the present invention is not limitedto the usage. For example, the present invention may be applied to asystem using the CDMA for both the uplink and the downlink similarly tothe currently available WCDMA system, a system using the OFDM for boththe uplink and the downlink, or the like.

In the first to seventh embodiments stated above, the random accesschannel is applied to the uplink wireless channel. However, the scope ofthe present invention is not limited to the application. Alternatively,the present invention is applicable to any wireless channels used forcausing each base station to set transmission power information to eachmobile station, and for causing the mobile station to transmit uplinkdata at arbitrary timing at a power set based on the designatedtransmission power information.

In the first to seventh embodiments stated above, the base stationtransmits the RACH transmission power information over the BCH as thesystem information. However, the scope of the present invention is notlimited to the transmission method. For example, the base station maynotify each of the mobile stations of the RACH transmission powerinformation using an individual control signal.

Furthermore, in the first to seventh embodiments stated above, the basestation sets only one transmission power information. However, the scopeof the present invention is not limited to the setting. For example, themobile stations in one cell are divided into a plurality of groups, andthe base station may set different transmission power information to therespective groups. Namely, such a setting may be considered that thebase station sets a higher RACH transmission power to a user groupenjoying prioritized services than those set to the other ordinary usergroups. In another alternative, the base station may set the RACHtransmission power to different values according to contents of datatransmitted from the respective mobile stations. Namely, differentvalues may be set to the transmission power information in case of theabove-stated Reservation Request and that in case of transmission of theuser data, respectively.

Moreover, in the first to seventh embodiments stated above, the basestation updates the RACH transmission power or the power offsetaccording to the transmission delay estimation information. However, thescope of the present invention is not limited to the update method. Thebase station may update the transmission power or the power offset usingthe other information. For example, one of factors for increasing thetransmission delay is as follows. Because of heavy RACH traffic (becauseof the larger number of mobile stations intended to transmit data overthe RACH), a plurality of mobile stations transmit data or a preambleover the RACH at the same timing and a collision occurs. In such a case,since the insufficient RACH transmission power does not possibly causean increase in the transmission delay, there is no need to increase theRACH transmission power or the power offset. In other words, the basestation estimates the RACH traffic from the number of mobile stationssuccessfully transmitting the data or preamble over the RACH in apredetermined time or the like. Only if the RACH traffic is equal to orsmaller than a predetermined threshold, the base station may update thetransmission power or the power offset based on the transmission delayestimation information as described in the first to seventh embodiments.

The invention claimed is:
 1. A mobile station comprising: a receiverconfigured to receive first information from a base station; and atransmitter configured to: transmit, to the base station, a first RACHpreamble based on the first information, wherein the first RACH preambleis transmitted without second information, the second information beingrelated to a number of RACH preambles sent until a successful RACHcompletion; and transmit the second information to the base station,wherein the receiver is configured to receive third information from thebase station, the third information being changed from the firstinformation based on the second information, wherein the transmitter isconfigured to transmit, to the base station, a second RACH preamblebased on the third information, and wherein the second RACH preamble istransmitted without fourth information, the fourth information beingrelated to a number of RACH preambles sent until a successful RACHcompletion.
 2. The mobile station according to claim 1, wherein thetransmitter is configured to transmit the second information to the basestation after transmitting the first RACH preamble.
 3. The mobilestation according to claim 1, wherein the receiver is configured toreceive the third information after transmitting the second information.4. The mobile station according to claim 1, wherein the transmitter isconfigured to transmit the second information to the base station afterreceiving a signal from the base station.
 5. The mobile stationaccording to claim 4, wherein the signal is a response to the first RACHpreamble.
 6. The mobile station according to claim 1, wherein thetransmitter is configured to transmit the first RACH preamble withpreamble transmission power, the preamble transmission power beingdetermined by the mobile station using the first information.
 7. Themobile station according to claim 1, wherein the transmitter isconfigured to transmit the second RACH preamble with preambletransmission power, the preamble transmission power being determined bythe mobile station using the third information.
 8. A method of a mobilestation, the method comprising: receiving first information from a basestation; transmitting, to the base station, a first RACH preamble basedon the first information, wherein the first RACH preamble is transmittedwithout second information, the second information being related to anumber of RACH preambles sent until a successful RACH completion,transmitting the second information to the base station; receiving thirdinformation from the base station, the third information being changedfrom the first information based on the second information; andtransmitting, to the base station, a second RACH preamble based on thethird information, wherein the second RACH preamble is transmittedwithout fourth information, the fourth information being related to anumber of RACH preambles sent until a successful RACH completion.
 9. Themethod according to claim 8, wherein the second information istransmitted to the base station after transmitting the first RACHpreamble.
 10. The method according to claim 8, wherein the thirdinformation is received after transmitting the second information. 11.The method according to claim 8, wherein the second information istransmitted to the base station after receiving a signal from the basestation.
 12. The method according to claim 11, wherein the signal is aresponse to the first RACH preamble.
 13. The method according to claim8, wherein the first RACH preamble is transmitted with preambletransmission power, the preamble transmission power being determined bythe mobile station using the first information.
 14. The method accordingto claim 13, wherein the first information is related to initialpreamble power.
 15. The method according to claim 8, wherein the secondRACH preamble is transmitted with preamble transmission power, thepreamble transmission power being determined by the mobile station usingthe third information.
 16. A base station comprising: a transmitterconfigured to broadcast first information to a mobile station, the firstinformation being configured for transmitting a first RACH preamble; anda receiver configured to: receive the first RACH preamble from themobile station, wherein the first RACH preamble is received withoutsecond information, the second information being related to a number ofRACH preambles sent until a successful RACH completion; and receive thesecond information from the mobile station, wherein the transmitter isconfigured to broadcast third information to the mobile station, thethird information being configured for transmitting a second RACHpreamble, the third information being changed from the first informationbased on the second information, wherein the receiver is configured toreceive the second RACH preamble from the mobile station, and whereinthe receiver is configured to receive the second RACH preamble withoutfourth information, the fourth information being related to a number ofRACH preambles sent until a successful RACH completion.
 17. The basestation according to claim 16, wherein the receiver is configured toreceive the second information after receiving the first RACH preamble.18. The base station according to claim 16, wherein the transmitter isconfigured to broadcast the third information after receiving the secondinformation.
 19. The base station according to claim 16, wherein thereceiver is configured to receive the second information aftertransmitting a signal to the mobile station.
 20. The base stationaccording to claim 19, wherein the signal is a response to the firstRACH preamble.
 21. The base station according to claim 16, wherein thefirst information is configured for determining transmission power ofthe first RACH preamble.
 22. The base station according to claim 16,wherein the third information is configured for determining transmissionpower of the second RACH preamble.
 23. A method of a base station themethod comprising: broadcasting first information to a mobile station,the first information being configured for transmitting a first RACHpreamble; receiving the first RACH preamble from the mobile station,wherein the first RACH preamble is received without second information,the second information being related to a number of RACH preambles sentuntil a successful RACH completion; receiving the second informationfrom the mobile station; broadcasting third information to the mobilestation, the third information being configured for transmitting asecond RACH preamble, the third information being changed from the firstinformation based on the second information; and receiving a second RACHpreamble from the mobile station, wherein the second RACH preamble isreceived without fourth information, the fourth information beingrelated to a number of RACH preambles sent until a successful RACHcompletion.
 24. The method according to claim 23, wherein the secondinformation is received after receiving the first RACH preamble.
 25. Themethod according to claim 23, wherein the third information istransmitted after receiving the second information.
 26. The methodaccording to claim 23, wherein the second information is received aftertransmitting a signal to the mobile station.
 27. The method according toclaim 26, wherein the signal is a response to the first RACH preamble.28. The method according to claim 23, wherein the first information isconfigured for determining transmission power of the first RACHpreamble.
 29. The method according to claim 28, wherein the firstinformation is related to initial preamble power.
 30. The methodaccording to claim 23, wherein the third information is configured fordetermining transmission power of the second RACH preamble.
 31. A mobilestation comprising: a receiver configured to receive first informationfrom a base station; and a transmitter configured to: transmit, to thebase station, a first RACH preamble based on the first information,wherein the first RACH preamble is transmitted separately from secondinformation, the second information being related to a number of RACHpreambles sent until a successful RACH completion; and transmit thesecond information to the base station, wherein the receiver isconfigured to receive third information from the base station, the thirdinformation being changed from the first information based on the secondinformation, wherein the transmitter is configured to transmit, to thebase station, a second RACH preamble based on the third information, andwherein the second RACH preamble is transmitted separately from fourthinformation, the fourth information being related to a number of RACHpreambles sent until a successful RACH completion.
 32. A base stationcomprising: a transmitter configured to broadcast first information to amobile station, the first information being configured for transmittinga first RACH preamble; and a receiver configured to: receive the firstRACH preamble from the mobile station, wherein the first RACH preambleis received separately from second information, the second informationbeing related to a number of RACH preambles sent until a successful RACHcompletion; and receive the second information from the mobile station,wherein the transmitter is configured to broadcast third information tothe mobile station, the third information being configured fortransmitting a second RACH preamble, the third information being changedfrom the first information based on the second information, wherein thereceiver is configured to receive the second RACH preamble from themobile station, and wherein the receiver is configured to receive thesecond RACH preamble separately from fourth information, the fourthinformation being related to a number of RACH preambles sent until asuccessful RACH completion.
 33. A method of a mobile station, the methodcomprising: receiving first information from a base station;transmitting, to the base station, a first RACH preamble based on thefirst information, wherein the first RACH preamble is transmittedseparately from second information, the second information being relatedto a number of RACH preambles sent until a successful RACH completion;transmitting the second information to the base station; receiving thirdinformation from the base station, the third information being changedfrom the first information based on the second information; andtransmitting, to the base station, a second RACH preamble based on thethird information, wherein the second RACH preamble is transmittedseparately from fourth information, the fourth information being relatedto a number of RACH preambles sent until a successful RACH completion.34. A method of a base station, the method comprising: broadcastingfirst information to a mobile station, the first information beingconfigured for transmitting a first RACH preamble; receiving the firstRACH preamble from the mobile station, wherein the first RACH preambleis received separately from second information, the second informationbeing related to a number of RACH preambles sent until a successful RACHcompletion; receiving the second information from the mobile station;broadcasting third information to the mobile station, the thirdinformation being configured for transmitting a second RACH preamble,the third information being changed from the first information based onthe second information; and receiving the second RACH preamble from themobile station separately from fourth information, the fourthinformation being related to a number of RACH preambles sent until asuccessful RACH completion.